With advances in automation technology, it has become possible for many types of mechanical and electrical equipment to function without continuous observation and supervision by operating personnel. This development has been put to advantageous use in situations where equipment, such as that utilized in a pumping station, must be located in a remote, unpopulated area. In these instances, equipment automation at the remote site eliminates the substantial manpower and transportation costs which would be entailed in maintaining an on-site staff for attending the equipment.
Because unattended automated equipment may experience unexpected operational failure, some system for notifying service personnel of a failure is generally a necessity for most unattended systems. Without such a notification system, the equipment could be inoperative for lengthy periods of time before the malfunction comes to the attention of service personnel. Such notification systems have most frequently made use of pre-existing telephone networks, which offer a relatively inexpensive communication medium adaptable to equipment monitoring purposes.
Known in the art are systems in which equipment at a remote station is connected to a telephone network, so that the equipment may be monitored by telephoning the remote station. The ringing voltage received at the telephone terminal at the remote station actuates means for answering the call at the remote station, and thereafter the system causes a signal to be sent to the caller over the line, indicating the status of the equipment being monitored. Timer means may be provided at the remote station for terminating the telephone connection after a predetermined period has elapsed, so that the remote station may be re-called at a later time, without the need to maintain constant telephone contact with the remote station. Representative patents embodying systems of this type include: U.S. Pat. No. 1,765,598, issued to McCoy, et al.; U.S. Pat. No. 2,326,200, issued to Bristol; U.S. Pat. No. 3,347,987, issued to Chaloupka; U.S. Pat. No. 3,029,642, issued to Burhans, et al.; U.S. Pat. No. 3,989,898, issued to Dugan, et al.; and U.S. Pat. No. 4,016,360, issued to Cane. Also known are similar systems in which a telephone caller to a telephone terminal at the remote station may hear sounds produced adjacent the telephone set via the microphone in the terminal's handpiece. Representative patents embodying this type of system include U.S. Pat. No. 2,898,405, issued to Eck, and U.S. Pat. No. 3,038,965, issued to Civitano.
Prior art equipment monitoring systems have generally required both a means for creating an open telephone connection between a monitoring station and a remote station, and a means for terminating the connection upon the completion of information transmission between the remote and monitor stations. These requirements have been met by providing equipment for answering all incoming calls at the remote station, so that an open line may be formed, and for terminating the telephone connection after a predetermined time has elapsed, once information transmission over the open line is complete. The answering and timer equipment required in prior art equipment monitoring systems has contributed significantly to the cost of purchase, operation and maintenance of these systems.
While substantial amounts of information may be transmitted over the open telephone connection established in prior art monitoring systems, transmission of large amounts of information is not required in many types of equipment monitoring applications. For example, it may be necessary for monitoring personnel to know only whether equipment at a remote site is in proper operating condition, so that it may be determined whether to make a service call. In such a case, specific information as to the causes of operational failure, if any, need not be transmitted, since this information will ordinarily be obtained at the time of the equipment service call, if such a call is required. Because the only information required is whether or not the equipment is operational, most of the information-transmitting capability of prior art equipment monitoring systems would be wasted in such an application.
The small amounts of information which must be transmitted in many monitoring applications have not thus far been met with a less costly equipment monitoring system, in part because of the need for answering and timing equipment in all current systems. A need therefore exists for an equipment monitoring system in which an open telephone line between the remote and monitor stations is not required, so that the costly answering and timing equipment of prior art systems may be eliminated.